But he said when he spoke with the ex-PM in the months before the general election of 2010, he told him Whitehall officials “believe it’s their job to actually run the country”.

In a blog for Fox News, Mr Hilton said: “It was a fascinating conversation. Whatever you might think of his record, there’s no question that Blair is an incredibly impressive political figure with enormous experience.

“Blair was candid and thoughtful, and gave us a brilliant primer on what he’d learned about making the machinery of government work.

“But there was one thing above all that stood out from our conversation: his blunt warning about the administrative state and the attitude any incoming government would face from the permanent bureaucracy.”

PA

Former director of strategy in Number 10 said the ex-PM told him Whitehall officials ‘believe it’s their job to actually run the country’

He says Mr Blair told him: “You cannot underestimate how much they believe it’s their job to actually run the country and to resist the changes put forward by people they dismiss as ‘here today, gone tomorrow’ politicians.”

He said he then added: “They genuinely see themselves as the true guardians of the national interest, and think that their job is simply to wear you down and wait you out.”

Mr Hilton added: That, in a nutshell, is the Deep State.

“And Blair’s warning was prophetic, as I discovered even before Cameron took office as prime minister.”

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The “deep state” is a theory that there is in fact a secret government – which exists in the shadows – and is the real source of power, not the visible, elected Government figures.

His comments come after un-elected officials in the Treasury were accused by Tory MPs of trying to influence Brexit policy with last week’s leaked impact assessments.

One of the subjects of their anger is also the former head of the civil service Gus O’Donnell - who Mr Hilton also claimed in his blog that had tried to blunt Mr Cameron’s government transparency policy plans in 2010.

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What is the deep state and where does it operate?

THE "deep state" is a name for the idea that some countries are run by an unelected elite which is more powerful than democratic politicians.

Among the bodies sometimes described as being part of a deep state are the military, civil service and big business.

Deep states are usually thought to be a problem in poorer countries where democracy has not been established for very long.

For example, countries including Egypt, Thailand and Pakistan have seen elected governments overthrown when they defied the interests of established elites.

And Turkey suffered an attempted coup in 2016, apparently organised by military leaders angry with the country's president.

Some commentators have suggested the idea of a deep state also applies in a more subtle way to more developed countries such as Britain and the US.

They argue that politicians are stopped from enacting radical change by civil servants who are intent on defending the status quo.